Nanotribology of transition metal dichalcogenide flakes deposited by chemical vapour deposition: The influence of chemical composition and sliding speed on nanoscale friction of monolayers

We present nanoscale frictional analysis of three commonly used transition metal dichalcogenide (TMD) monolayers, WS2, MoSe2 and WSe2, deposited by chemical vapour deposition (CVD). The monolayers were characterised by Raman spectroscopy, photoluminescence spectroscopy (PL), and X-ray spectroscopy (XPS), to determine the composition of the coating and confirm monolayer structure. Nanoscale frictional analysis was performed by atomic force microscopy (AFM). Load-dependent frictional behaviour was measured at different sliding speeds to quantitatively assess friction on each sample. All samples experienced low nanoscale friction, with the lowest friction observed on WSe2. The friction was independent of sliding speed within the analysed range. Furthermore, monolayer TMDs significantly increase the operational load range by at least one order of magnitude when compared to SiO2 substrate.